Recently, as the fields of precise part fabrication and processing, semiconductor fabrication, microsurgery, gene manipulation, cell coordination and so on are more consumed and highlighted in the industries, medical circles and gene engineering, the study for developing and utilizing robots for precise works is very active.
A serial robot with an open link is one of manipulators widely used in the industries. The series robot allows a large working space and good workability, but it has bad precision since errors are accumulated at a terminal device due to drivers connected in series. In addition, the series robot has a drawback in that its dynamic efficiency is deteriorated during a high-speed work or while a load is greatly changing.
As an alternative for overcoming the drawback of the series robot, a parallel mechanism has been actively studied from 1980. The parallel mechanism has a closed chain, so its work place is relatively small. However, errors of the terminal devices are not accumulated due to drivers, and it may operate excellently even during a high-speed work or while a dynamic load is greatly changing due to high structural rigidity. Therefore, the parallel mechanism is more advantageous for precise working than the series mechanism.
The parallel mechanisms developed so far have terminals whose degree of freedom (DOF) is 3 or 6. Such DOF is deficient or excessive in comparison to DOF required for demanded works such as needling, and therefore the parallel mechanisms are inefficient and unsuitable for works such as needling in a 3D space.
Meanwhile, a haptic device for interaction between remote robot manipulation and virtual environment is actively studied recently. The haptic device is a bidirectional interface which plays a role of an input device for inputting the movement of a user to a controller of a system and a role of an output device for transferring a suitable force or touch to the body of a user according to an instruction of the controller.
Haptic devices are configured to use a handle connected to a terminal of a robot. Therefore, the haptic devices also have sensors and motors at every joint, measure position and posture of the terminal of the robot by the movement of the handle, and generate a force and torque of the terminal by driving a motor.
Forward kinematics which allows obtaining position and posture of the terminal from the location information of active joints is important so that the robot may be used by means of the haptic device. However, the haptic device using the series mechanism has the sensor and motor mounted to each joint, and therefore the motor is moved along with the moving haptic device. The movement of the motor increases the inertia of the device, which obstacles the movement of the user and increases the fatigue of the user.
In addition, if a master device used as the haptic device and a slave device driven by the master device have different DOFs, it is difficult to match working spaces of both devices. Therefore, in order to realize an efficient haptic device, it is demanded that the master device used as the haptic device has the same DOF as the slave device for the working space.